Why did Duolingo give a very big achievement task
Keeping all golden skills at a time is really tough!
I agree with OmegaGmaster.
Using the method in https://www.duolingo.com/comment/6176795/Best-Way-to-Make-Your-Tree-Turn-Gold-and-Stay-Gold is very efficient.
Every day I only need to do 2 - 10 strengthenings in Duolingo's web version to keep four trees gold.
I think it's supposed to be hard. Until the vocab is really ingrained it's easy to forget. Remember how long it took you to master your native tounge… But alas - I agree with you. I had all my skills golden but it took many hours of practice.. Enjoy the work - it pays off. Christel